Bull!
Show me a printed barrel that can stand 50,000 CUP pressure on a sintered metal printer. You can't. It would fly apart after 1 shot.
I don't have any examples of that part specifically, but there is a lot of research being done on metal printing, since there is a lot of interest from aerospace. Instead of just sintering the parts together, there is other post processing now to make the parts stronger. Here is one example:
Also, the part can probably be cast metal, so we could use a sand printer to create the mold and just cast it:
Keep in mind that a person doesn't have to completely recreate a commercial model in its exact specifications. If a part needs to be stronger because the printed material is weaker, the engineer may just need to make the critical part thicker.
I think it can be done, if not likely at 50,000 CUP. I believe I'd begin with a printed launcher for the GyroJet cartridge, produced by AAI and others, or a smaller version of the high-low pressure cartridge as used in the 40mm ammunition for the M79 and M203 grenade launchers. Even a single-shot low-cost *printed* 40mm blooper would be formidable. And of course it could be a one-shot disposable item like the WWII German Panzerfaust 60 or the American M72/M72A3 LAW family.
You are aware that during WWII, the British firm of Lines Brothers developed a process of stamping a barrel out of flat sheet metal plate, after which rifling was engraved upon it by means of diagonal milled grooves, followed by rolling the flat along a mandral and then fusion welding the barrel seam closed.
If not terribly elegant or traditional, the process resulted in a barrel suitable for use with the 9mm Sten submachinegun, and lowered the production costs for that weapon down to the vicinity of $6.00 U.S. each, less than the seven magazines that accompanied each guns.
Most of the Lines Brothers Mark III guns were airdropped to friendly partisan forces or used as secondary armament in Brit fighting vehicles. But there are those who reckon the Mk III design is considerably more reliable than the predecessor MKII despite the manufacturing shortcuts.